Sheets or other webs of material are used in a variety of industries and in a variety of ways. These materials can include paper, multi-layer paperboard, and other products manufactured in long webs and collected on reels. Web manufacturing or processing systems typically include multiple actuators positioned across a web being manufactured or processed. The direction across the web's width is called the cross direction, and the direction along the web's length is called the machine direction.
Cross direction (CD) alignment refers to the spatial relationship between centers of individual CD actuators' zones and centers of downstream CD web quality measurements. It is often an important parameter used to model a web manufacturing process, and it typically affects the performance of a feedback CD controller.
Conventional CD alignment identification techniques often rely on open-loop “bump” or “step” tests. During these tests, operation of a feedback CD controller is suspended, and multiple actuators are perturbed to new positions. Actuator setpoint profiles, web quality measurement profiles, or other data values are sent to a software tool, which runs an open-loop identification algorithm that returns a linear or nonlinear function quantifying the existing CD alignment.
Unfortunately, switching the feedback CD controller on and off interrupts the system's normal operation, and there is often no control over web qualities during open-loop tests. As a result, open-loop tests are often not preferred in practice. Also, many web manufacturing or processing system operators often depend on manual observation of misalignment symptoms in webs before starting an alignment identification test.